Why do vendors who provide FIX protocol connectivity require a static IP address? Is the only reason user identification/validation? Or is there any other reason behind that?
Thanks
Yes, the reason is that the (free registration required, sadly) FIXT specification test cases (specifically test case 1S/c) requires IP validation for Logon messages. It does not exclude the possibility of allowing an entire IP block (just references "system configuration" as a source of the allowed IP), but most vendors follow the spirit of highest possible security.
The spec (page 39) further mentions unauthorized attempts to break into your system as the reason for doing the validation.